Preparation of metallated and substituted alkynes

ABSTRACT

A process is provided for making metallated and substituted alkynes from feedstocks which include alkadienes containing allenic unsaturation or such alkadienes in a mixture with alkynes having either internal or terminal unsaturation, such as a mixture of propadiene and propyne. This reaction involves an initial step in which the allenic hydrocarbon and any internal alkyne is isomerized and simultaneously the resultant terminal alkynes are metallated with an alkali metal. The reaction is carried out at relatively low temperatures in a suitable inert solvent such as diethylether. When metallation is complete the reaction mixture can be contacted directly with any suitable electrophile, such as a halo silane, for example, chlorotrimethylsilane, and the alkali metal on the terminal alkyne is replaced with the desired substituent. The products thus formed are useful as monomers for preparing polymers having a variety of properties, for example, as asymmetric membranes for gas separation.

This is a division, of application Ser. No. 07/513,133, filed Apr. 23,1990 now U.S. Pat. No. 5062998.

FIELD OF THE INVENTION

This invention relates to the simultaneous isomerization and metallationof allenic hydrocarbons. In another aspect, it relates to themetallation of a mixture of alkyne and allenic hydrocarbons in thepresence of an allene isomerization catalyst. In yet another aspect, itrelates to the conversion of these metallated products to substitutedalkynes which can then be converted into useful polymers.

BACKGROUND OF THE INVENTION

Recent developments in the use of polymers of substituted alkynes havefocused interest on the preparation of such monomers. For example,poly-1-(trimethylsilyl)-1-propyne is very attractive in preparingmembranes for gas separations. The monomer is prepared by metallatingpropyne with butyllithium followed by reaction withchlorotrimethylsilane. The fact that propyne is very expensive hasadversely affected the economics of these substituted acetylenicpolymers. One approach to reduce the cost of such polymers and otherderivatives of substituted alkynes has been to use an impure source ofalkynes as a feedstock. This approach is illustrated in U.S. 3,752,848,Smith (1973), which describes making tetrolic acid (2-butynoic acid) byintroducing carbon dioxide into a slurry of propynyl alkali metal, suchas propynyl sodium, and then hydrolyzing the carbonated slurry. Thepatent states that the unrecovered product slurry produced by the methodof U.S. Pat. No. 3,410,918, Beumel, et al. (1968) can be used as thesource of the propynyl alkali metal compound after disappearance of thealkali metal particles and cooling to below 8O° C. The '918 patentdescribes the preparation of propynyl sodium and propynyl lithium byreacting propyne with sodium or sodium/lithium dispersions. A mixture ofpropyne and allene in a weight ratio of about 1:1 to 4:1 is used as thefeedstock and the allene remains relatively inert so as not to interferewith the propyne metalation. Some propyne is said to be hydrogenated topropane. The propyne/allene feedstock is cheaper than pure propyne.

The feedstock such as that referred to by the '918 patent is actuallyavailable commercially as a cutting fuel and is referred to as MAPP gas,having a composition of about 23 to 36% propyne, 18 to 28% propadieneand 1 to 8 wt. % propylene and butenes.

Although it is known that propadiene can be isomerized to propyne, thisapproach has not been used to increase the value of such mixedfeedstocks. U.S. Pat. No. 3,671,605, Smith (1972) discloses isomerizingallenes into acetylenic isomers at temperatures of -10° to 100° C.,using a catalyst of sodium or potassium reacted with alumina. Lithium issaid to be inoperable. Alumina is reacted with molten alkali metal withagitation and under an inert gas blanket. The allene, such aspropadiene, may be pure or mixed with its acetylenic isomer, forexample, propyne. In either case the product is said to be anequiIibrium mixture in which the acetylenic isomer predominates.

Dykh, et al., Izv. Akad. Nauk SSSR. Ser. Khim, (1978), 11, 2473,disclose that allene can be isomerized to methyl acetylene on metaloxide and zeolite catalysts. Various aluminas were used at temperaturesof 20° to 350° C. Isomerization of methyl acetylene to allene alsooccurs and the kinetics of the forward and reverse reactions arediscussed.

Khulbe, C.P.; Mann, R. S., Can. J. Chem. (1978) 56, 2791, discloseequilibrium constants for the isomerization of allene to methylacetylene and discuss this reaction catalyzed with silica-supportedcobalt and iron.

The isomerization of allenes is also disclosed in U.S. Pat. No.4,036,904 Strope (1977) which describes purifying a 1,3-butadiene streamprior to catalytic cyclodimerization when the stream contains alleneswhich would poison the dimerization catalyst. Allene and 1,2-butadieneare converted to acetylenic compounds over a magnesium oxide catalyst at85° to 355° C. Allene is converted to methylacetylene and 1,2-butadieneis converted to 2-butyne or 1,3-butadiene.

Brown, C.A.; Yamashita, A., J. Am. Chem. Soc., (1975), 97, 891 disclosethat potassium 3-aminopropylamide rapidly catalyzes the isomerization ofalkynes having interior triple bonds to 1-alkynes. Macaulay, S.R., Can.J. Chem., (1980), 58, 2567 discloses sodium aminopropylamide withsomewhat higher temperatures is more effective than the reagent ofBrown, et al. The materials studied were decyn-1-ol and its isomers.Abrams, S.R., Can. J. Chem. (1982) 60, 12238 states that isomerizationsreported by Brown and Yamashita can be carried out with catalysts whichare sodium salts of 1,3-diaminopropane or 1,2-diamino ethane. Use of thereagents is disclosed for isomerizing acetylenic acids.

Abrams, S. R., Can. J. Chem., (1984) 62 1333 describes an improvement inthe catalysis of triple bond migration in isomerizations to formterminal alkynes and alkynols over the earlier work with catalysts whichwere sodium salts of 1,2-diaminoethane or 1,3-diaminopropane. Theimproved catalysts are lithium salts of these compounds with theaddition of sodium or potassium alkoxides, such as potassiumtert-butoxide.

In summary, the conversion of alkadienes by isomerization to terminalacetylenes is well known and a variety of isomerization catalysts areavailable for this procedure. Such isomerization of allenes is alsosuggested in Hotitz, et al., J. Orq. Chem. (1973) 38, 489 and by Abrams,et al., J. Org. Chem. (1987) 52, 1835.

SUMMARY OF THE INVENTION

We have now found that a process for making metallated 1-alkynes can beaccomplished by reacting, in an inert solvent under low temperatureconditions., i.e. less than about 50° C., for allene isomerization andalkyne metallation, an allenic hydrocarbon of 3 to 8 carbon atoms withan alkali metal and allene isomerization catalyst. The isomerizationreactions involving allenic hydrocarbons and alkynes, such as propadieneand propyne, are equilibrium reactions that are reversible. In otherwords the catalysts which convert allenic hydrocarbons to alkynes havingterminal unsaturation, also isomerize the terminally unsaturated alkyneto the feedstock hydrocarbons. By carrying out a simultaneousmetallation in an inert solvent, such as ethyl ether, under mildconditions of temperature which previously have not been reported, e.g.,below about 50° C., the 1-alkyne is metallated as it is formed andeffectively removed from the equilibrium mixture. In this manner, forexample, all of the C₃ H₄ hydrocarbon in a propyne/propadiene feedstock,can be converted to metallated propyne which can then in turn beconverted to a substituted propyne useful as a polymerization monomer.Terminal alkynes can also be present in the reaction mixture, in whichcase they are metallated at said low temperature conditions, whichheretofor have not been reported in the prior art.

The invention also includes making substituted alkynes by first reactingin an inert solvent under conditions for allene isomerization an allenichydrocarbon having 3 to 8 carbon atoms optionally also containing analkyne having 3 to 8 carbon atoms with an alkali metal and alleneisomerization catalyst, thereby forming a metallated 1-alkyne andthereafter allowing the mixture to react with an electrophile, leaving asubstituent on the alkyne.

DETAILED DESCRIPTION OF THE INVENTION

Substituted alkynes having 3 to 8 carbon atoms per molecule, andparticularly substituted propynes, are monomers which can be convertedinto polymers possessing a variety of useful properties. These polymerstend to be very expensive, however, in part because of the high cost ofthe alkyne which is used to prepare the monomer. The present inventionprovides a convenient, low cost procedure which can be carried out intwo steps in one reaction vessel without intermediate reaction work-upto obtain substituted alkynes, particularly propynes, from inexpensivefeedstocks, such as the commercially available MAPP gas, which containsboth propyne and propadiene. The procedure of the invention convertsboth of these unsaturated hydrocarbons to the desired substitutedalkyne, first by a simultaneous isomerization/metallation reaction andsubsequently by substitution of the metal with a suitable electrophilethat can react with the alkynylmetal species.

The isomerization reactions involving allenic hydrocarbons and alkynes,such as propadiene and propyne, are equilibrium reactions that arereversible. In other words the catalysts which convert allenichydrocarbons to alkynes having terminal unsaturation, also isomerize theterminally unsaturated alkyne to the feedstock hydrocarbons. By carryingout a simultaneous metallation in an inert solvent, such as ethyl ether,under mild conditions of temperature which previously have not beenreported, e.g., below about 50° C., the 1-alkyne is metallated as it isformed and effectively removed from the equilibrium mixture. In thismanner, for example, all of the C₃ H₄ hydrocarbon in apropyne/propadiene feedstock, can be converted to metallated propynewhich can then in turn be converted to a substituted propyne useful as apolymerization monomer. The fact that the entire procedure can becarried out in one reaction vessel also offers economic advantages inreducing the costs of equipment and operations.

In accordance with the present invention, a substituted alkyne havingthe general structural formula:

    R.sup.1 --C|C--R.sup.2

where R¹ is alkyl or aralkyl having 1 to 8 carbons and R² is a silyl,germyl, alkanol or alkanone substituent, is produced in a solvent,preferably diethyl ether, according to a two step, one-pot procedure.Examples of alkynes which can be so substituted include methylacetylene,ethylacetylene, pentyne-1, 3-methylbutyne-1, hexyne-1,3-phenyl-1-propyne and the like.

The first step, for example, involves metallation/isomerization of apropyne/propadiene mixture in the presence of an alkali metal,preferably sodium, and one of the following catalysts: either an alkylamine, preferably an alkyl diamine, more preferably 1,3-diaminopropanein combination with an alkali metal base such as a hydride or analkoxide; or a metal oxide, preferably magnesium oxide. This is followedby reaction of the intermediate propynylmetal derivative with anysuitable electrophile RX where X may be a leaving group such as Cl, Br,I and the like R is a silane, germane, alkyl, aldehyde or ketonesubstitute. Alternatively, the propynylmetal derivative can be combinedwith an unsaturated group (e.g., carbonyl) which can undergo reductionvia reaction with the propynylmetal species.

In a typical reaction, 1.0 molar equiv. of sodium metal is combined withthe appropriate amount of isomerization agent, either 0.02 to 5.0 equiv.of magnesium oxide, or 0.02 to 1.0 equiv. of 1,3-diaminopropane in thepresence of an additional alkali metal base such as a hydride oralkoxide, in diethyl ether and the mixture is cooled to between -40° and-70° C. The C₃ H₄ hydrocarbon gas stream (1.0 to 2.0 molar equiv. of thereactive component(s)) is introduced all at once and the mixture isallowed to warm gradually to room temperature over 1 to 3 hours,continually recondensing the volatile hydrocarbon into the etherealsolution by means of a dry ice/isopropanol condenser. The resultantpropynylsodium slurry is then treated with (1.0 to 2.0 molar equiv.) ofthe electrophile. Time and temperature for complete reaction with theelectrophile is dependent upon electrophile structure.

The following examples illustrate that propadiene portions of a C₃ H₄hydrocarbon feedstock afford substituted propynes under the givenconditions.

EXAMPLE 1

Magnesium oxide (2.2 g; vacuum oven dried at 400° C. for several hours)and freshly prepared sodium metal (0.6 g; finely divided) were combinedin 25 ml of diethyl ether (distilled from CaH₂) and cooled to -40° C.Pure propadiene (1.5 g) was introduced and the mixture was allowed towarm to room temperature with stirring for an additional 2 hours.Benzyldimethylchlorosilane (4.4 g) was added all at once and thereaction was allowed to proceed at room temperature for 15 hours.Aqueous 10% HCl was added dropwise to destroy any residual sodium metal.The product was then extracted with pentane and concentrated to afford3.6 g (80%) of crude benzyldimethylsilylpropyne. The purity of the crudepropyne product was high as indicated by ^(l) H NMR.

EXAMPLE 2

Sodium metal (0.6 g; finely divided), 1,3-diaminopropane (0.1 g; freshlydistilled), and potassium hydride (0.05 g) were combined in 25 ml ofdiethyl ether (distilled from CaH₂) and cooled to -70° C. Purepropadiene (2.0 g) was introduced and the mixture was allowed to warm toroom temperature with stirring for an additional 2 hours.Benzyldimethylchlorosilane (4.4 g) was added all at once and thereaction was allowed to proceed at room temperature for 15 hours.Aqueous 10% HCl was added dropwise to destroy any residual sodium metal.The product was then extracted with pentane and analyzed by gaschromatograph (GC) /mass spectrometry (MS) . Results showed the productto be benzyldimethylsilylpropyne and no allenic product was observed.

EXAMPLE 3

A run was carried out to demonstrate the metallation of propyne at lowtemperatures. Sodium metal (1.1 g; freshly cut to expose clean surface)was cooled to -78° C. in 50 ml of diethyl ether. Propyne (7.5 g, 0.19mol) was introduced and the reaction mixture was allowed to warm andstir at room temperature for an additional 3 h.Benzyldimethylchlorosilane (8.8 g,0.048 mol) was added dropwise over 15min and the reaction was allowed to proceed for an additional 15 h. HCl(50 ml) was added to destroy any residual sodium metal, the product wasextracted with three 50 ml portions of pentane, then concentrated anddried to afford 9.1 g of crude benzyldimethylsilylpropyne. The purity ofthe crude product was very high as indicated by ^(l) H NMR.

Examples 4 and 5 describe the procedure for the synthesis of1-(trimethylsilyl)-1-propyne, a monomer of interest because of itspolymer, poly-1-(trimethylsilyl)-1-propyne.

ILLUSTRATIVE EXAMPLE 4

Sodium metal (0.6 g; finely divided) is combined with magnesium oxide(2.2 g; vacuum oven dried at 400° C. for several hours) in 25 mL ofdiethyl ether (distilled from CaH₂) and the mixture is cooled to -40° C.The propadiene/propyne gas mixture (2.0 g; containing about 70% C₃ H₄hydrocarbon) is introduced all at once and the mixture is allowed towarm gradually to room temperature over 1 hour, continually recondensingthe volatile hydrocarbon into the ethereal solution by means of a dryice/isopropanol condenser. The resultant propynylsodium slurry is thentreated with chlorotrimethylsilane (3.1 g) and the reaction is allowedto proceed at room temperature for 15 hours. Aqueous 10% HCl is addeddropwise to destroy any residual sodium metal. The product is thenextracted with pentane and the organic extract distilled with carefulfractionation to obtain 1-(trimethylsilyl)-1-propyne.

ILLUSTRATIVE EXAMPLE 5

The procedure of Example 3 is repeated using 1,3-diaminopropane (0.1 g)and potassium hydride (0.05 g) as the isomerization catalyst instead ofmagnesium oxide.

These examples give representative catalysts, reagents and reactionsolvents for the preparation of substituted alkynes fromalkyne/alkadiene/hydrocarbon mixtures and are not meant to be limitingin any way.

A wide variety of electrophiles will react with the intermediatepropynylmetal species. The appropriate choice of electrophile dependsupon the structure of the desired product. For example, just as1-(trimethylsilyl)-1-propyne is prepared according to the procedure setforth in Examples 4 and 5 by the addition of chlorotrimethylsilane tothe propynylsodium slurry, a number of other acetylenic monomers (e.g.,1-(ethyldimethylsilyl)-1-propyne, 1-(phenyldimethylsilyl)-1-propyne,1-(trimethylgermyl)-1-propyne, as well as 2-butyn-4-ols and alkylsubstituted propynes can be prepared by treatment of the propynylmetalderivative with the appropriate halosilane or germane, aldehyde, ketone,or alkyl halide.

In addition to the use of sodium as a metallating agent, other alkalimetals (e.g., lithium, potassium) are also effective.

Aromatic hydrocarbon solvents such as benzene, toluene, xylene, orethylbenzene, aliphatic hydrocarbons such as hexane or octane andethereal solvents including tetrahydrofuran, dioxane, ethylene glycoldimethyl ether and ethylene glycol diethyl ether can be used instead ofdiethyl ether as the reaction solvent.

A variety of primary and secondary amines and diamines will isomerizealkadienes to alkynes in the presence of an alkali metal hydride oralkoxide. Suitable isomerization catalysts include 1,3-diaminopropane,alkylamines such as methylamine and dimethylamine, alkyl diamines suchas 1,2-diaminoethane, 1,2-diaminopropane, 1,4-diaminobutane and1,2-diaminocyclohexane, aryl amines such as aniline, and aryl diaminessuch as 1,2-,1,3- or 1,4-phenylene diamine, and the like.

Also useful as the isomerization catalyst are magnesium oxide and otherGroup IIA (alkaline earth) oxides (e.g., CaO) as well as Group IIIB(e.g., La₂ O₃) and Group IVB (e.g., ZrO₂) oxides. Additionalalternatives include the above oxides and those of Groups IIIA and IVA{e.g . . . , Al₂ O₃, SiO₂) treated with alkali metals or alkali metalsalts such as hydroxides and carbonates. See Tanabe, K., "Solid Acidsand Bases", Kodansha, Tokyo, Academic Press, New York, 1970 and Pines,H.; Stalick, W. M., "Base Catalyzed Reactions of Hydrocarbons andRelated Compounds", Academic Press, New York, 1977 for comprehensivereviews of suitable solid state isomerization catalysts.

Other aspects and embodiments of our invention will be apparent to thoseskilled in the art from the foregoing disclosure without departing fromthe spirit or scope of the invention.

We claim:
 1. A process for making substituted alkynes whichcomprises:(a) contacting in an inert solvent under conditions for alleneisomerization an allenic hydrocarbon having 3 to 8 carbons which analkali metal in the presence of an allene isomerization catalyst,thereby forming a metallated 1-alkyne, and (b) adding to the reactionmixture of step (a) containing said metallated 1-alkyne, an electrophileselected from the group consisting of a halosilane, halogermane, alkylhalide, aldehyde and ketone, which undergoes reaction with saidmetallated 1-alkyne to form said substituted alkyne.
 2. A process formaking substituted alkynes which comprises:(a) contacting in an inertsolvent under conditions for allene isomerization a mixture ofhydrocarbons, at least one of which is an alkyne having 3 to 8 carbonatoms and an allenic hydrocarbon having 3 to 8 carbons with an alkalimetal and an allene isomerization catalyst, thereby forming a metallated1-alkyne, and (b) adding to the reaction product of step (a) containingsaid metallated alkyne, an electrophile selected from the groupconsisting of a halosilane, halogermane, alkyl halide, aldehyde andketone, which undergoes reaction with said metallated alkyne to formsaid substituted alkyne.
 3. The process of claim 2 wherein saidisomerization catalyst is (a) an oxide of a metal of Groups IIA, IIIB orIVB, or (b) an oxide of a metal of groups IIA, IIIA, IVA, IIIB or IVB ofthe Periodic Table previously treated with an alkali metal or an alkalimetal salt, or (c) an alkyl or aryl amine with an alkali metal hydrideor alkoxide.
 4. The process of claim 2 wherein said alkyne is propyne,said allenic hydrocarbon is propadiene, said alkali metal is sodium,said isomerization catalyst is magnesium oxide and said electrophile ischlorotrimethylsilane.
 5. The process of claim 2 wherein said alkyne ispropyne, said allenic hydrocarbon is propadiene, said alkali metal issodium, said isomerization catalyst is 1,3-diaminopropane with potassiumhydride and said electrophile is chlorotrimethylisilane.
 6. The processof claim 2 wherein said solvent is ethyl ether and the reactions ofsteps (a) and (b) are carried out below 50° C.